Sen. Bernard Sanders, I-Vt., has joined 23 other senators in challenging the postmaster general’s authority to stop Saturday mail service without congressional approval.

On Feb. 6, Postmaster General Patrick Donahoe announced the U.S. Postal Service will no longer deliver regular mail Saturdays starting in August, saving about $2 billion per year. Packages, express mail and medications would continue to be delivered, and local post offices would remain open Saturdays.

The Postal Service has seen its revenues fall dramatically largely because more and more people are corresponding by email.

Sanders and the other senators sent a letter to Donahoe on Friday saying they knew the Postal Service was in dire financial straits, but urged him to work with Congress to fix the problem.

The letter read, in part: “It appears that as recently as last year, the Postal Service did not believe it had the authority to end six-day delivery without legislative action by Congress. ... We request that you provide a detailed legal justification for this proposed change.”

In a recent appearance on Vermont Public Radio’s “Vermont Edition” to talk about the Postal Service and other issues facing Vermont, Sanders said: “What most people don’t know is that 80 percent of the financial problem of the Postal Service has to do with the fact that they were asked by Congress in 2006, in a very, very bad provision, to pay $5.5 billion every single year for future retirees’ health care. No other entity in the government, no other entity in the private sector has been asked to come anywhere near close to that kind of financial commitment.”

Last week, Sanders and Rep. Peter DeFazio, D-Ore., introduced Senate and House legislation that would allow the Postal Service to generate new revenues by providing additional services — including the issuing of hunting and fishing licenses, notary public services and shipments of wine and beer.

The bill would also repeal the 2006 health care provision for future retirees.

The legislation would also help postal customers “take advantage of email and Internet services,” according to Sanders, although details were not disclosed.

His statement said the bill would preserve Saturday delivery and put in place safeguards to protect rural post offices from being shut down.

It would also create a commission made up of “successful business innovators and representatives from small business and labor” that would make recommendations to help the Postal Service generate more revenue and continue to evolve in the digital age.

Sen. Patrick Leahy, D-Vt., and six other senators joined Sanders as co-sponsors of the Senate version of the bill.